1. Field of the Invention
The present invention relates generally to a system for regulating the output of a vehicle alternator. More particularly, the invention relates to a method and system for optimizing the output of the vehicle alternator so as to minimize vehicle fuel consumption.
2. Background Art
Alternators are used in conventional motor vehicles to convert mechanical energy produced by the vehicle""s internal combustion engine to electrical energy. Alternating current (AC) generated by the alternator""s rotating shaft is converted to direct current (DC), which in turn is used to power vehicle electrical circuits during normal driving conditions and to charge the vehicle""s battery.
In order to protect and properly operate the electrical circuits and charge the battery, the amount of charge or current provided by the alternator must be properly regulated. Accordingly, conventional regulating devices have been developed to maintain the DC alternator output voltage, or xe2x80x9csetpoint,xe2x80x9d within a nominal range, typically 12 to 15 volts. Conventional regulating devices, as disclosed for example in U.S. Pat. Nos. 5,711,605 and 6,018,234, use either inferred or actual battery temperatures to regulate the alternator voltage output.
A problem with conventional devices however is that corresponding regulation strategies are not tunable or adaptable to changing load demands of the vehicle. As such, an appreciable amount of mechanical energy is often converted to excess electrical energy, and thus energy is lost that can otherwise be used to drive or power other vehicle systems or components. The expended mechanical energy is most basically in the form of engine torque, which in turn requires a greater expenditure of fuel to satisfy the artificially high electrical loads of the vehicle.
In addition, mechanical energy is also lost in the form of heat due to the unnecessary charging of the vehicle battery at higher voltage levels than what is actually required. Increased heat losses translate into decreased efficiency and thus further increased fuel consumption. Damage to the battery can also occur under such conditions due to battery gassing.
Further, because more fuel is burned, an increased amount of engine exhaust is generated requiring addition emissions control measures.
Accordingly, the inventors herein have recognized the need to provide an improved system and method for regulating the output of a vehicle alternator so as to minimize vehicle fuel consumption and emissions and reduce the risk of damage to the vehicle battery.
The aforedescribed limitations of conventional voltage regulation methods and systems are substantially overcome by the present invention, in which a method for operating an alternator of a motor vehicle is provided. The method includes the steps of monitoring an amount of stored electrical energy available to operate the vehicle, estimating a vehicle electrical load, and regulating an output of the alternator based at least in part on the amount of electrical energy available to the vehicle and the estimated vehicle electrical load. Preferably, the alternator setpoint voltage is regulated based on a measured battery state of charge and the estimated electrical load of the vehicle.
A corresponding system for operating an alternator of a motor vehicle is also disclosed. The system includes a first monitor for indicating the amount of stored electrical energy available to operate the vehicle, a second monitor for indicating operation of vehicle electrical components, and a controller coupled to the first and second monitors for estimating a vehicle electrical load based on operation of the vehicle electrical components and for regulating an output of the alternator based at least in part on the indicated amount of stored electrical energy and the estimated vehicle electrical load.
An advantage of the above-described method and system is that the alternator output can be regulated so as to minimize vehicle fuel consumption. For example, by taking into account the battery state of charge and the electrical energy required by the vehicle at any given time, an alternator setpoint voltage can be optimized so as to more closely track the electrical load requirements of the vehicle and thus minimize the amount of excess electrical energy generated. By optimizing the setpoint, based at least in part on the amount of stored electrical energy and estimated vehicle load, mechanical energy otherwise used to produce excess electrical energy is conserved and used for other purposes thereby providing a fuel economy gain when operating the vehicle.
Further objects, features and advantages of the invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.